When aerial refueling began 90 years ago, it was self-serve. The first to gas up in mid-air was U.S. Navy Lieutenant Godfrey Cabot, who, while skimming the Potomac River in a Huff-Daland HD-4, used a grappling hook on the fuselage to snatch a five-gallon can of fuel from a float in October 1921.

Air-to-air, gravity-fed fueling came along two years later when Army Air Corps pilots at Rockwell Field in San Diego used one de Havilland DH-4B to refuel another via a 50-foot rubber hose. But in-flight gassing didn’t become routine until the Korean War.

“I think of two eras: 30 years of stunts and experimentation, followed by 60 years of operational use,” says Jim McCormick, who manages aerial refueling research for the Defense Advanced Research Projects Agency.

It was the need to station U.S. jet fighters in Korea and to give the Strategic Air Command’s bombers the capacity to make non-stop round trips to the Soviet Union that drove the progress of aerial refueling. By late 1950, two devices had been developed to give the tanker’s feed line stability in the airstream: a drogue, or basket, shaped like a shuttlecock, at the end of a fuel hose, and a telescoping boom. (The boom can feed fuel six times faster than a drogue and can do so at higher speeds and in worse weather. )

“The equipment and techniques have been improved to make in-flight refueling safer and more effective, but the systems have not changed radically,” says McCormick. On Boeing KC-767 tankers, operators use advanced consoles near the cockpit with remote controls and camera monitors that enable them to fly the booms more precisely in low visibility or darkness. Greater use of simulators during training is also making refueling safer.

Today, researchers are gauging the feasibility of refueling unmanned aircraft. The Air Force Research Laboratory and Boeing’s Phantom Works are investigating boom technology with a manned KC-135R tanker and a Learjet modified to fly unmanned in tests set to run until 2013. Meanwhile, DARPA and NASA studied drogue systems using a pair of F/A-18As configured for pilot-less flight; those tests, which proved the viability of automated refueling, ended in 2007.

Next spring, DARPA plans to fly a Global Hawk UAV in the first high-altitude tests of one unmanned aircraft using a drogue to refuel another. McCormick predicts that any refinements in the technology will eventually be used in piloted aircraft.